1. Field of the Invention
This invention relates generally to apparatus and method for biologic reagent deposition. More particularly, this invention relates to apparatus and method for applying a micro-fabrication method for enabling high-speed deposition of large number of biologic reagent spots with low cost micro-fabricated stamps.
2. Description of the Prior Art
Several technical challenging difficulties are still confronted by those who apply conventional methods and apparatuses to form micro-arrays of biological samples on a support to perform analyses of a large number of biological reagents. The first challenge is the requirement to form a very large number of biological samples within a relatively short time to prevent over-evaporation or characteristic changes due to long time atmosphere exposure of the samples after micro array deposition. This requirement is often a limitation when analyses are performed on micro array consisted of more then ten thousands samples. Due to the sequential nature in dispensing a defined volume of liquid samples over the surface of a biological bindable surface, the deposition process may take more than one hour to complete even with the aid of computer controlled automation. Additionally, in order to obtain meaningful comparisons between the reactions among many deposited biologic samples on a biological bindable surface, the size and location for each of the biological samples must be precisely controlled. Several processes employed for depositing large number of biological samples in parallel experience greater degrees of random variations in sample sizes and are not very useful for practical applications. Beyond these difficulties, for purposes of biological sample testing, it is often desirable to deposit the biological samples of different sizes among the great number of biological samples. As the following brief review will clearly illustrate that current state of the art in making arrays of biological macromolecules, such as nucleic acid or proteins, do not have sufficient technical capabilities to satisfy all these requirements.
As discussed by D. J. Harrison, in “The Preface of the Proceedings of μTAS” (Banff, Canada, pp. Vii-viii, October 1998), the array-based system and the micro-fluid system are two major technologies employed for the analyses of a large number of biological reagents. One major task for such operation is to manipulate tiny amount of biological fluid. In the array-based technology, the biological samples or reagents are deposited in large arrays on a plate or chip for parallel biological processing and analyses. In the array-based technology, the quality of sample deposition plays a key role in determining the results of the biological analyses.
Brown et al disclosed in U.S. Pat. No. 5,807,522, entitled “Methods for Fabricating Micro-arrays of Biological Samples” (issued on Sep. 15, 1998), a method and apparatus for forming micro-arrays of biological samples on a support. As that shown in FIG. 1, the method involves dispensing a known volume of a reagent 16 at each selected array position by tapping a capillary dispenser on the support under conditions effective to draw a defined volume of liquid onto the support. The apparatus is designed to produce a micro-array of such regions in an automated fashion controlled by computer or microprocessors. Even with fully automatic control, this method is limited by a sequential nature of the sample dispensing processes that requires a longer period of time to complete the sample-deposition operations. The dispensing apparatuses and the micro-range movement machine and control processor are also very expensive and require high level of design and manufacture technologies to provide such devices and control system. As S. D. Rose discussed in the paper “Novel Tools for Creating and Reading DNA Microarrays” (Microdevices for Biomedical Applications, San Jose, Calif. April 1999), Brown's method takes at least one hour to spot over one chip with ten-thousand biological spots. And the system costs more than twenty-five thousand dollars ($25,000) for parts. The spots deposited with this method have about 20% size variation and if used for protein spotting, the spots may lose function to due sample drying out due to the long spotting cycle.
Other methods include photolithography (J. F. Mooney et al. “Patterning of Functional Antibodies and Other Proteins by Photolithography of Silance Monolayers” Proc, Natl. Acad. Sci. USA 93, pp 12287-12291, 1996, as shown in FIG. 2A-1 to 2A-3). Another paper presented a method of ink jet printing (D. Wallace et al. MHS'97, Nagoya, Japan, October 5-8, p 129, 1997 as shown in FIG. 2B-1 to 2B-4). B. Martin et al. disclosed a micro-stamping method (“Direct Protein Micro-Array Fabrication Using a Hydogel Stamper” (The American Chemical Society Journal of Surfaces and Colloids” Jul. 21, 1998, Volume 14, Number 15 as shown in FIGS. 2C-1 to 2C-4). Floch et al. (1998) and Y. Xia et al. (1996) disclosed a PDMS method as that shown in FIGS. 2D-a to 2D-e and FIGS. 2E-1 to 2E-5. All these methods encounter the difficulties that either the selection of sample types is limited, or having complexity on fabrication or operation processes thus become inconvenient or too expensive to be practically useful for large scale biological sample array analyses.
Therefore, a need still exists in the art of apparatus and operation techniques of biological sample deposition for a new and improved method to overcome these difficulties and limitations.